1. Field of the Invention
The present invention relates to a method of and apparatus for generating a pulse signal.
2. Description of the Related Art
It is necessary to generate a pulse signal in response to the position or speed of a moving object or pulse signals in response to various operations in automatic controls or electric or electronic equipment. An example is an electromagnetic pickup among various pulse signal generators of this type. This electromagnetic pickup consists of a magnetic element, magnets, and an electric coil such that movement of an object changes the magnetic density which, in turn, generates a voltage in the electric coil by electromagnetic induction. This voltage is used as a pulse signal.
This electromagnetic pickup, however, has the following disadvantages. When the object to be detected moves at a very low speed, the generated voltage is as low as the noise level. Consequently, it is necessary to provide a filter circuit in front of an amplifying circuit to eliminate noise before amplification. Conversely, when the speed of a moving object is very high, the generated voltage exceeds the maximum voltage of an amplifying circuit and needs a limiter. On the case of low speed, it has been proposed that an auxiliary ring having an enlarged diameter is attached to the object to increase the peripheral speed for detection. However, this proposition makes the equipment larger and the number of components larger. In addition, if the speed varies, the rising or falling time varies. The detection of more accurate timing requires a complicated signal process. Moreover, the waveform of the voltage depends on the shape of the object.
Another example is a position, angular, or speed sensor using Hall effects such as shown in Japanese patent application Kokai No. 2-284082. This Hall effect type sensor employs a Hall element and a magnet. Movement of the object to be detected changes the magnetic flux to the Hall element which, in turn, generates an electrical signal. This sensor, however, needs a separate power source to energize the Hall element. The generated electrical signal is not pulse but sinusoidal. Where the speed of an object is low, the rising voltage is decreased and the waveform is crashed. Like the above electromagnetic pickup, this sensor is prone to not only external magnetic field but also thermal drift and noise. In order to provide more accurate detection signal, a complicated processor circuit is required.
Japanese patent application Kokai No. 54-161257 discloses a pulse signal generator for use as a sensor. This pulse signal generator comprises a magnetically sensitive element made from a ferromagnetic body which consists of a relatively soft and magnetically anisotropic section and a relatively hard section, a first magnetic field source for magnetizing the magnetically sensitive element in the positive direction, a second magnetic field source for magnetizing the relatively soft section in the negative direction, a detection coil provided near the magnetically sensitive element, and a movable body for intermitedly reducing the magnetization of the magnetically sensitive element by the first magnetic field source. Movement of the movable body causes a predetermined change in the magnetically sensitive element thereby generating a pulse voltage in the detection coil.
This pulse signal generator needs no power source and provides constant pulse voltages when the object moves at very low speeds and is resistant to external magnetic field. Thus, it solves some of the problems presented by the electromagnetic pickup and Hall effect type sensor.
The conventional pulse signal generator, however, has the following disadvantages, has limited applications, and is not practical. First of all, it needs a movable body having slits. It is impossible to make the movable body smaller than the first and second magnetic field source and the magnetically sensitive element. The slits are provided in the movable body radially so that the diameter of the movable body must be large. In addition, the movable body, the magnets, and the magnetically sensitive element must be parallel to each other. The magnets are so prone to external magnetic fields or metals that the operation is unstable. The generator is not always interchangeable for the electromagnetic pickup or Hall effect type sensor because of the special relationship with the object. For example, it is impossible to dispose it to detect the teeth of a gear directly.
Accordingly, it is an object of the invention to provide improvements in the pulse signal generating method and apparatus.
According to one aspect of the invention there is provided a method of generating a pulse signal, comprising the steps of providing a pair of magnetic field sources in parallel to each other such that their opposite poles are faced to each other; providing a magnetic element between the parallel magnets; advancing an object from one of the opposite poles to the other to thereby change a magnetic field applied to the magnetic element, which causes a large Barkhausen jump in the magnetic element; and generating a pulse signal in response to the large Barkhausen jump.
According to another aspect of the invention there is provided a pulse signal generator comprising a magnetic element able to cause a large Barkhausen jump; detection means for detecting a magnetic change in the magnetic element to generate a pulse signal; and a pair of magnetic field sources provided in parallel to each other on opposite sides of the magnetic element such that their opposite poles are faced to each other so that when an object advances from one of the opposite poles to the other, a magnetic field applied to the magnetic element changes to cause a large Barkhausen jump in the magnetic element, thus causing the detection means to generate a pulse signal.
According to an embodiment of the invention there is provided a pulse signal generator, the magnetic field sources consist of parallel magnets and magnetic circuit forming members.
According to another embodiment of the invention there is provided a pulse signal generator which further comprises an auxiliary magnetic circuit forming member for connecting the magnetic circuit forming members at other ends which are opposite to the one ends.
According to still another embodiment of the invention there is provided a pulse signal generator, wherein the auxiliary magnetic circuit forming member is connected to the magnetic circuit forming members at varying points.
magnets have a width greater than that of the object.
According to yet another embodiment of the invention there is provided a pulse signal generator, wherein the magnetic element is spaced at an end thereof from the auxiliary magnetic circuit forming member by a predetermined distance.
According to an embodiment of the invention there is provided a pulse signal generator, the magnetic field sources consist of only parallel magnets.
According to another embodiment of the invention the pair of poles has a variable distance.
According to still another embodiment of the invention the magnets have a width greater than that of the object.
According to yet another embodiment of the invention the magnetic element extends from the one end of the magnets to a predetermined distance from the other end of the magnets.
According to an embodiment of the invention the predetermined distance is no more than one half of the magnets.
According to another embodiment of the invention the magnetic element extends at a predetermined angle with a longitudinal direction of the magnets.